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Calibrating dome thermometer

I recently replaced my dome thermometer that had cracked a long time ago (I think a squirrel dropped an acorn onto it from the tree branch high above the egg).

I hadn't calibrated the new thermometer at first and noticed that even with a full load of lump running with bottom vent wide open and no cap on the top, the dome temp didn't get above 650. This seemed strange based on my previous experience, so I tested the thermometer in boiling water and it read somewhere in the 150 range, so I knew something was up. I calibrated the thermometer by adjusting the nut on the back and got it to read 212 in boiling water. Problem is now even at room temp it reads about 125 (it's not nearly that hot in NY).

Are BGE thermometers just really inaccurate at low temps (i.e. room temperature or ambient temperature out of direct sun) and as long as it reads boiling water to be 212, I'm fine, or is this a bigger issue that I should be concerned about, particularly at low-and-slow cooking temps?

That's the problem--I don't know if it reads correctly in normal operating temps (other than 212). I have no way of knowing if it's still accurate at 250, 300, etc (short of applying some of that chemistry I learned in school and doing a boiling point elevation experiment with a lot of solute dissolved in the water).

I never worked sales (or any other dept) for a furniture company, but I'm now curious as to why you asked? Is there another Aron with one A running around somewhere?

Do you have a leave-in meat probe thermometer? If so you can put it in through the dome thermometer hole and compare it to your egg thermometer reading. Or you can simply stick both of them through the holes on the daisy wheel. You are right, just because you can adjust the nut to read 212 in boiling water does not mean it will read correctly at 350. There is no mark on the egg thermo for 32 degrees, but you can place it in a cup of ice water and if it reads approximately the right distance below 50 degrees it will give you an idea if it is at least close to accurate.

I'll definitely give the ice water test a try just to see what happens.

I hadn't tried the leave-in meat probe since I had no idea what it's upper level temp range would be. I know it reads at least up to about 200 since I've cooked brisket to an internal temp of 200 before, but don't want to damage that probe if it's not meant to go much higher. Any idea what an average leave-in probe reads up to? I'm pretty sure mine is a maverick.

I'm on my second Egg thermometer. Last weekend, my egg seemed to be running below temp, using more fuel and the butt was miraculously done in 9 hours. I checked the calibration the next day and it was running 170 at boiling so I adjusted it like you.

Then the therm was reading 100+ for ambient air temp when it was 75ish. I have the same question about the reliability of the "calibrated" thermometer since it is clearly off at lower temps now. I know it's good at 212f but worry about accuracy at 350, 450, etc.

Mine just keeping exposed to a lot of moisture since my Egg cover leaks like a sieve.

I am ordering a couple from Tel Tru to see if they hold up any longer. (And I'm going to remove it while the Egg is covered;) )

I haven't done it yet, but it occurred to me that the next time I deep fat fry something using my Taylor mercury thermometer (which I trust) I should bring in the Egg thermometers and see what they read at 375º.